Staphylococcus aureus is an opportunistic pathogen of man and domestic animals that is both readily amenable to genetic analysis (by transduction and transformation) and is a relatively typical Gram positive pathogenic bacterium. Not only are several of its mechanisms of pathogenicity relatively well characterized, but the genetic determinants for pathogenicity is determined in part by chromosomal and in part by plasmid-borne genetic determinants. The primary goal of this proposed research is to define the genetic linkage group that constitutes the chromosone of S. aureus. This objective will be met primarily by means of genetic transformation analysis, and will concentrate on nutritional and antibiotic-resistance determinants as selected markers; unselected markers of interest will include the ability to elaborate coagulase, fibrinolysin, the various hemolysins, heat-stable nuclease, and enterotoxin. A second primary objective is to further our understanding of the transformation reaction (i.e., competence) in staphylococci. At this writing, three major linkage groups have been defined on the chromosome, together with at least one site of prophage and plasmid integration. Competence for transformation has been shown to be a potential property of the majority of coaguluse-positive staphylococci, and to be dependent on a helper-phage phenomenon. BIBLIOGRAPHIC REFERENCES: Pattee, P.A. 1976. Linkage of the genetic determinants of tetracycline resistance, purine and isoleucine biosynthesis, and pigmentation in Staphylococcus aureus. Abstr. Ann. Mtg. Amer. Soc. Microbiol. 1976:H10. Pattee, P.A. 1976. Genetic linkage of chromosomal tetracycline resistance and pigmentation to a purine auxotrophic marker and the isoleucine-valine-leucine structural gene in Staphylococcus aureus. J. Bacteriol. 127: 1167-1172.